This invention relates generally to story books and voice recording devices and more particularly to a combination story book and voice recording device.
Digital recording units convert an audio signal to a digital format creating a digital audio file. The digital audio file is stored, and a playback converts the digitally stored file back to sound audio for playback.
Digital audio is the method of representing audio in digital form.
An analog signal is converted to a digital signal at a given sampling rate and bit resolution; it may contain multiple channels (2 channels for stereo or more for surround sound). Generally speaking: the higher the sampling rate and bit resolution the more fidelity. Both systems introduce noise at the capturing stage, in analogue recording this is due to the noise floor of the circuit, and in digital recording due to quantization noise.
Much like an analog audio system, a digital audio system strives to reproduce the audio perfectly but neither can ultimately prevail. Analog systems have inherent capacitance and inductance which limit the bandwidth of the system and resistance limits the amplitude. Digital systems' sampling rate limits the bandwidth and bit resolution limits the dynamic range (resolution of amplitude creation). Both systems require increased cost and attention to achieve higher fidelity.
A digital audio signal starts with an analog-to-digital converter (ADC) that converts an analog signal to a digital signal. The ADC runs at a sampling rate and converts at a known bit resolution. For example, CD audio has a sampling rate of 44.1 kHz (44,100 samples per second) and 16-bit resolution for each channel (stereo). If the analog signal is not already bandlimited then an anti-aliasing filter is necessary before conversion, to prevent aliasing in the digital signal. (Aliasing occurs when frequencies above the Nyquist frequency have not been band limited, and instead appear as audible artifacts in the lower frequencies).
Some audio signals such as those created by digital synthesis originate entirely in the digital domain, in which case analog to digital conversion does not take place.
After being sampled with the ADC, the digital signal may then be altered in a process which is called digital signal processing where it may be filtered or have effects applied.
The digital audio signal may then be stored or transmitted. Digital audio storage can be on a CD, an iPod, a hard drive, USB flash drive, CompactFlash, or any other digital data storage device. Audio data compression techniques—such as MP3, Ogg Vorbis, or AAC—are commonly employed to reduce the size. Digital audio can be streamed to other devices.
The last step for digital audio is to be converted back to an analog signal with a digital-to-analog converter (DAC). Like ADCs, DACs run at a specific sampling rate and bit resolution but through the processes of oversampling, upsampling, and downsampling, this sampling rate may not be the same as the initial sampling rate.
The DAC fundamentally converts finite-precision numbers (usually fixed-point binary numbers) into a physical quantity, usually an electrical voltage. Normally the output voltage is a linear function of the input number. Usually these numbers are updated at uniform sampling intervals and can be thought of as numbers obtained from a sampling process. These numbers are written to the DAC, sometimes along with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched resulting in a piecewise constant output. This is equivalently a zero-order hold operation and has an effect on the frequency response of the reconstructed signal.
Piecewise constant signal is typical of a practical DAC output. The fact that practical DACs do not output a sequence of dirac impulses (that, if ideally low-pass filtered, result in the original signal before sampling) but instead output a sequence of piecewise constant values or rectangular pulses, means that there is an inherent effect of the zero-order hold on the effective frequency response of the DAC resulting in a mild roll-off of gain at the higher frequencies (a 3.9224 dB loss at the Nyquist frequency).
The prior art teaches the use of, so called “talking books” but does not teach a combination story book and detachable audio device for recording the storyline of each story book whereby the audio playback is initiated from a light sensor and does not require any action on the part of the reader to initiate playback, other than opening the front cover.